The present invention relates to grids for bringing about the spacing of a group of sheathed fuel rods in a nuclear reactor, particularly a water reactor or a vast neutron reactor, said grids serving to maintain the rods parallel to one another and in accordance with a given system, whilst also ensuring the elastic support of said rods in accordance with various successive regions distributed according to their length, particularly for the purpose of preventing vibrations thereof under the action of the circulation of a liquid cooling medium flowing in contact with said rods.
Numerous spacing grid designs of this type are known, being in particular formed by an assembly constituted by two groups of thin perforated sheets which are parallel within each group and perpendicular from one group to the next. These sheets are indented at regular intervals so as to permit their fitting to one another, thus defining cavities with a square cross-section, each of which is traversed by one rod of the group. In order to ensure the necessary elastic support on these rods the sheets are appropriately cut and shaped in such a way as to have towards the inside of each cavity bosses in relief and tongues which form springs, whereby each rod in a cavity is applied to two fixed supports provided on one of the sheets under the action of the sprung tongue provided in the parallel opposite sheet.
In another improved construction in order to combine the advantages of satisfactorily maintaining the elasticity of the tongues under irradiation and a low neutron absorption of the spacing grid the perforated sheets with their fixed supports are made from a slightly absorbing material, for example "Zircaloy" and the sprung tongues from another material, for example "Inconel", the latter being connected to the sheets and immobilised relative thereto by means of appropriate fixing means.